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From: "Richard Sohn" <res12@fairpoint.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2952398@logan.com>
Subject: Re: [FlyRotary] Re: combined starter alternator
Date: Wed, 4 Jun 2008 08:18:40 -0500
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----- Original Message ----- 
From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, June 03, 2008 9:44 PM
Subject: [FlyRotary] Re: combined starter alternator


> Richard Sohn wrote:
>> I do not have the direct answer to your question, it would be too long, 
>> however, the first two cars I owned had a starter-generator set up. The 
>> first one was a 700cc DKW model 1938 and the other one was a 1949 DKW, 
>> sort of a post war successor. Both were two cylinder two strokes. It had 
>> an outside armature on the crank shaft with a set of brushes on a disc 
>> type commutation. Once the engine was running, it worked as a generator 
>> through a separate exciter winding in the stator, controlled through the 
>> voltage regulator. The windings on the armature were used as starter and 
>> generator. There was frequently a problem with cranking, because it was 
>> loosing torque with the slightest voltage drop in the system.
>> I do not believe that such a system could be built competing, at least 
>> weight wise, with a gear reduction starter motor. As a mater of 
>> principle, a high torque electric motor is always heavier than a high 
>> speed motor producing the same torque through gear reduction. And, of 
>> course, at the same hp.
>>
>>
> I'm not disagreeing, Richard, but I'd like to point out that the system
> isn't just competing with the gear reduced starter, weight-wise.  It's
> competing with the starter, an alternator, and all the pulley, belts and
> mounting hardware.
>
> The last few years have produced some substantial advancements in
> permanent magnet motors.  Mostly the introduction of neobyium (sp?)
> magnets, that have given them useful power output.  The biggest problem
> is that you need multiple horsepower from a starter to crank an engine,
> but only need the generator to produce fractional HP.  I think the
> problem could be solved by a PM motor that used relays to energize
> several coils for starting, but only utilized a fraction of those for
> charging.  Getting the requisite torque from a motor can be accomplished
> by gearing it down, or by giving it a larger diameter.
>
> Here is what I think is the start of the solution.  A Harley generator.
> The stator is bolted up to the rear of the PSRU.  I still need to build an 
> adapter to match the rotor to the flywheel/clutch-plate.
>
> http://ernest.isa-geek.org/Delta/Pictures/EnginePSRUInitialMounting.jpg
> http://ernest.isa-geek.org/Delta/Pictures/EngineGeneratorFitting.jpg
>
>Ernest,

this is certainly a good way to go, for several reasons. My concerns are 
only with the starter side of the issue.

One word of caution on the neodium(?) magnets. As off today, their magnetism 
is very temperature sensitive, like, stay below 100C or you will loos it.

Richard Sohn
N2071U
>
> http://www.ronpaultimeline.com
>
>
>
>
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